Optical Clocks for ESA Deep Space Ground Stations

Transcription

1 Optical Clocks for ESA Deep Space Ground Stations Hugh Klein National Physical Laboratory, NPL, UK with Location and Timing KTN U.K.

2 NPL led study for Started July 2006 Feasibility and applications of optical clocks as frequency and time references in ESA deep space stations Patrick Gill, Geoff Barwood, Hugh Klein, Helen Margolis, Stephen Webster, (NPL) Fritz Riehle, Ekkehard Peik, Harald Schnatz, Uwe Sterr (PTB), Wolfgang Schäffer, Gerhard Hejc, Alexander Pawlitski & Diana Portolés, (TimeTech) Jens Hammesfahr, Johann Furthner, Alexandre Moudrak & Matthias Süss (DLR)

3 Outline Optical clocks; state of the art and projected capability Deep space ground stations; environmental issues Specification of ground station optical clocks Other space applications of optical clocks Conclusion and future activity Optical clocks offer better stability and potential accuracy than microwave clocks Stable laser for space - - History: 1999 DJEK & HAK etc.bio etc.

4 Optical clocks instability σ Δf 1 f (S/N) Based on forbidden optical transitions in atoms or ions Optical frequencies are 10 5 times higher than microwave Q-factor (or even higher) Diddams et al Science (2001) Reference - Atoms or Trapped Ion(s) + Oscillator - Ultra-stable Laser + I ( f ) f 0 0 Counter - Femtosecond comb f

5 Neutral Atom lattice clock Sr mhz-wide 1 S 0 3 P 0,2 clock transitions available, much narrower than the 1 S 0 3 P 1 intercombination transitions in Ca (370 Hz) and Mg (30 Hz) Long interrogation times better stability, but how to hold the atoms? Fountains or ballistic expansion not so good! Problems still remain with residual Doppler shifts, cold collisional shifts and < 1 sec interrogation times Optical lattice trapping sites

6 Neutral Atom lattice clock Sr Optical Lattice idea (Katori 2001) 3D off-resonant standing wave laser field Light-shift generated trapping sites with sub-λ spacing Long interaction times, many atoms 1 st order Doppler effect eliminated (Lamb-Dicke regime) Collisional shifts small if 1 atom per site How to deal with AC stark shift (light shift) Optical lattice trapping sites

7 PTB Sr neutral lattice clock CCD camera for absorption pictures Red cooling lasers Zeeman slower Optics for dipole trap PTB Sr neutral physics package: vac chamber for 2 stage cooling in magnetooptical trap and lattice trap Blue cooling laser source

8 Optical frequency standards compared to microwave 1.0E E-10 Essen's Cs clock iodine-stabilised HeNe Fractional uncertainty 1.0E E E E E E-16 H Cs redefinition of the second Ca H Microwave atomic clocks Cs fountain clocks Optical frequency standards H Hg +,Yb +,Ca Sr + Yb + Hg + Hg + /Al + Year 1.0E Optical clocks offer better stability and potential accuracy than microwave clocks

9 Deep Space Station Location of T&F rack next to maser room Quote from ESA statement of work Deep Space missions can feature round-trip delay times (propagation time ground-spacecraft-ground) up to a few hours. In this environment, accurate spacecraft positioning measurements require that ultra stable frequency references are used and distributed to ground segment equipment. At present, ESA deep space antennas are equipped with Hydrogen-Masers, which exhibit very good stability over typical propagation times

10 Stability Stability specification requested: 1 second; 100 seconds; 10,000 seconds optical-µw fibre comb Sr Boyd 2006 cavity cryo Maser optical µw Bartels 2005 Ca-Hg + Yb + -Yb + Al + -Hg τ (s)

11 Motivation Quote from ESA statement of work The advent of optical clocks will hopefully open the field to an outburst of new applications and mission returns. Deep Space Antenna Networks will particularly benefit from such instruments. Beyond the obvious improvement in spacecraft tracking capabilities, unprecedented radioscience work will be designed and tested, increasing our knowledge of the solar system in various topics, such as gravitational waves, solar wind, relativity, planetary gravitational waves, radio sounding of atmosphere, atmospheric absorption and bistatic radar.

12 JPL/NASA reference

13 Integration of optical clock into a deep space station Scenarios considered: Replace the H-maser by an optical clock, keeping existing interfaces at 100 MHz Operation of optical clock in noise-reduced, well-controlled environment outside the direct antenna vicinity of the ground station Operate the optical clock together with the H-maser and/or a cryogenic oscillator, to provide eg maser back-up for optical clock Examination of environmental conditions within DSN ground stations give strong steer for optical clock room away from the antenna (eg 100 m distance)

14 Optical frequency standards with high Q ~10 15 Atom based standards (e.g. Sr, Hg, Yb, Mg, Ca, Ag & H) Lattice used to trap atoms Lamb Dicke confinement Stark shift minimised by using magic wavelength Blackbody shift may be a systematic issue Beams and fountains less attractive Ultimate stabilities and accuracies beyond a part in are projected

15 Optical frequency standards with high Q ~10 15 Trapped ion standards (e.g. Sr +, Yb +, Hg +, In +, Ca +, Al + ) No 1st-order Doppler shift; Minimum 2nd-order Doppler shift Lamb Dicke confinement Field perturbations minimised at trap centre and background collision rate low Long interaction times; electron shelving technique (quantum jumps) - high detection efficiency Ultimate stabilities and accuracies beyond a part in are projected

16 Environmental requirements for optical clocks Temperature reproducibility: o C Vibration (acceleration): Acoustics (re 20 μpa): Magnetic fields < 2 μg/ Hz below 1 Hz, rising to < 30 μg/ Hz above 10 Hz, (1 μg is 10 μm/s 2 ) db over Hz see later discussion for ions These environmental requirements are more stringent than currently encountered in the Cebreros ground station.

17 Strontium ion traps at NPL Mumetal shields ~ 60 cm ~20 cm ~ 100 cm ~ 50 cm Present NPL endcap traps: Dimensions 50 to 100 cm Compact trap system mock up

18 Volume, Mass and Power of optical clocks Volume: Physics package Electronics package Ion clock 0.9 m m 3 (2 racks) Neutral atom clock 1.6 m m 3 (2 racks) Mass: Physics package Support structures Optimised support Electronics Total 74 kg 170 kg 85 kg 145 kg 400kg 123 kg 250 kg 125 kg 180 kg 550 kg Power: < 1.5 kw < 2.5 kw Transportability Sub-systems demountable Sub-systems demountable

19 Study recommendations Choice of reference for clock technology: Ions: 88 Sr + Atoms: Sr Environmental considerations: Location of optical clock in sub-surface building remote from antenna Distribution: Within antenna room: 10 GHz distribution frequency via cable Optical clock to antenna: microwave modulation of optical carrier via buried optical fibre is suggested Ranging: Antenna mechanical noise is dominant error Tropospheric contribution to error needs to be resolved

20 Study recommendations ctd. Proposed specification included: Choice of trapped 88 Sr + ion or Sr atom lattice for reference Physics package: 300 to 430 kg Volume 2.7 to 3.7 m 3 Power: 1.5 to 2 kw Magnetic field stability/reproducibility at trapped Sr + ion case: ~ s 300 nt / hr (assuming 1-layer mu-metal x30 shielding minimum) Four year breadboard development plan outlined Stability: 1 sec; 100 sec; 10,000 sec

21 Space applications of optical clocks Tests of Special and General relativity Tests of stability of fundamental constants Gravity wave detection Star and planetary survey using very deep baseline interferometry Time keeping Ground stations Pictures courtesy of ESA

22 Cosmic vision proposals with optical clocks Cosmic Vision Space science for Europe Two proposals using optical clocks to do Gravitational red shift and other fundamental physics experiments Search for anomalous gravitation using Atomic sensors SAGAS Proposes on-board Sr + ion optical clock Einstein Gravity Explorer (EGE) Optical and microwave clocks

23 Proposed missions using optical clocks ctd: Stephan Schiller et al. Precision tests of general relativity and of the equivalence principal using ultrastable optical clocks: a mission proposal Proc 39 th ESLAB Symposium Noordwijk April Suggests very stringent multiple tests of both relativistic theory (special and general) and the stability of fundamental constants Will require lasers that are both ultra-narrow (linewidth below one Hz), and very stable Highly eccentric orbit Potential for up to four orders of magnitude improvement over present tests

24 Realisation of SI unit of Time optical clocks in space Optical redefinition of the second The ultimate clocks for realising the second may have to be in space: to reduce fluctuating geoid related gravitational red shifts. issues at 3 x10 17 level See: Daniel Kleppner, March 2006 Physics Today Time Too Good to Be True. An optical redefinition of the second is likely. Time keeping beyond a part in may require clocks in space

25 NPL led studies for Started February 2006 Optical Frequency Synthesizer for Space-Borne Optical Frequency Metrology Patrick Gill, Hugh Klein Helen Margolis (NPL) Theodor Hänsch, Marc Fischer, Ronald Holzwarth, Andreas Sizmann (Menlo Systems) Volker Klein (KT), and Stefan Schiller (HHUD) Analysis of missions which would benefit from optical technology Workshop on Optical Frequency Combs for Space held at NPL October 2006: Fundamental science candidate mission selected

26 Absolute long distance measurement Absolute long distance measurement with (sub)-micrometre accuracy for formation flight applications Started October 2006 Detailed design of femtosecond-based distance metrology systems for the purposes of the Darwin and the Xeus missions. Detailed investigation of individual technologies and refinement of preliminary HAALDM concepts.

27 NPL involvement in space time and frequency projects Study and Breadboarding of a Sapphire Oscillator for Ultra-High Short-Term Stability Galileo Time Service Provider (TSP) & Precise Time Facility (PTF) algorithm work

28 People and politics FT 24/11 Guardian 27/1

29 Developments in optical clock components GROUND STATIONS Need transportable systems Reduced size Reliability Challenging! SPACE Size volume and weight reduced Power requirements reduced All components space qualified: Radiation tolerant or shielded Must survive launch Very Challenging!